1. Field of the Invention
The present invention relates to a method and system for enhancing image sharpness and, in particular, to a method and system for optimizing the sharpness quality of pictures during coding and image enhancement processes.
2. Description of the Related Art
It is the ultimate goal of video experts to provide most perceptually appealing video images to viewers. Sharpness is related to the clarity of detail in a video image and strongly depends on the edge definition of an image. The relative sharpness of an image can be measured, in the spatial domain, by the definition of edges in comparison to a reference image, or in the transformed domain, by the difference in high frequency energy associated with edges and fine details, also with respect to the reference. As one skilled in the art can appreciate, the quantization of the DCT coefficients of 8×8 blocks causes loss of content that affects sharpness while introducing blocking artifacts during an MPEG/JPEG encoding process. Although the blocking artifacts can be reduced without losing the edge information, the loss of sharpness resulting from DCT quantization is not recoverable through post-processing.
Accordingly, the present invention proposes a method of calculating the loss of sharpness caused by the quantization, then using this loss criterion to selectively adjust the quantization parameter to preserve the sharpness of the image during the video-coding process.